The invention concerns a press device for web-shaped material, and particularly for removing water from a web of paper in a paper machine. More particularly, the invention relates to an extended nip press.
A press device includes a stationary tubular support body that is supported around a stationary beam. A flexible, elastic shell extends around the support body and moves around it. A press shoe in the support body presses the shell against a counter roller or mating roller. The press shoe has a circumferentially elongate concave surface for defining an extended press nip with the counter roller. The press nip is formed relatively long in the circumferential direction. Pressure is exerted on a web of paper, which passes through the press nip together with a felt belt. The web and felt travel over a longer path of travel in an extended press nip than in a traditional roll press that consists of two rolls. In other words, higher "press momentum" (product of the press pressure times the time of pressure) is exerted on the web of paper than in a standard press nip.
Federal Republic of Germany Application DE-OS No. 31 26 492 shows guiding the press shoe for radial displacement directly in a flexing support beam or shows combining the press shoe and the flexing beam into a single structural part. A support body for also guiding the elastic shell outside of the press zone is not present.
In U.S. Pat. No. 4,287,021, a press shoe (formed in two parts) is also guided for radial movement directly within a flexing beam. The pressure within a pressure chamber located between the flexing beam and the press shoe is variable so as to adjust the press force. For the guidance of the elastic shell, which is open toward the outside at both of its edges, a support body is used. However, this reference does not suggest that the body rests on the flexing beam. It is merely guided on the outer sides thereof. Thus, it is not possible in this case to control the sag of the support body by means of the flexing beam.
The present invention is an improvement upon the press device shown in FIG. 5 of Federal Republic of Germany Application DE-OS No. 31 02 526. In that device, a press shoe is arranged on a roll-shaped support body that is in the form of a hollow beam. The press shoe is movable radially relative to the support body. Also, the support body is movable radially with respect to a supporting beam that is capable of flexing. Therefore, hydraulic pressure chambers are necessary between both the flexing beam and the support body supported by the beam and between the support body and the press shoe. This results in a relatively high structural expense. Furthermore, the two pressure-chamber systems, which are arranged in series, may lead to a lack of stability.